The os intermetatarseum is an uncommon accessory ossicle of the foot occurring in ~4% (range 1-7%) of the population.
It is usually asymptomatic and an incidental finding although it can be a cause of dorsal midfoot pain.
The os intermetarseum is typically positioned dorsally between the bases of the first and second metatarsals but has been reported to occur near the metatarsal heads or between the fourth and fifth metatarsal bases. It can have a variety of shapes:
- resemble a rudimentary metatarsal
It can be classified into three basic types:
- free standing: it is a completely independent ossicle, and it does not show any osseous or articular connection with any structure
- articulating: it may form a synovial joint with first or second metatarsal or the medial cuneiform
- fused: it forms a spur that is seen as a bony projection in the first and second intermetatarsal space